1. Field of the Invention
The present invention relates to an HVAC system for an automotive vehicle and more specifically to an HVAC system having an independent defroster control system.
2. Description of Related Art
To prevent fogging to an interior of a vehicle windshield, the temperature of the vehicle windshield needs to be above the dew point. Hot or warm (heating) air must be directed to the windshield in order to keep the temperature of the windshield above the dew point. In a conventional HVAC system the heating air is directed through an HVAC housing to one of several air outlets. Specifically, the heating air must be directed to a defroster outlet to heat the interior of the vehicle windshield to either defrost the windshield or remove fog from the windshield. A disadvantage, however, to the current HVAC system is that the temperature of the air and the volume of the air exiting the defroster outlet cannot be controlled independently of the temperature of the air and the volume of the air exiting other air outlets in the system.
For example, FIG. 1 shows a schematic view of a conventional HVAC system 100 for an automotive vehicle. The HVAC system 100 includes an HVAC housing 102, a blower (not shown), an evaporator 104, a heater core 106, an air mixing door 108, a mixing chamber 110, an airflow path 112, a defroster door 114, a defroster air outlet 116, a vent door 118, a vent air outlet 120, a heater air outlet 122, and an air outlet mode actuator 124.
The HVAC system shown in FIG. 1 has several modes of operation including defroster mode, heater (or foot) mode, and heater/defroster mode. After air from the evaporator 104 and the heater core 106 is mixed in the mixing chamber 110, the air flows through the airflow path 112 and exits through one or more selected air outlets depending on the selected mode of operation. For example, if heater mode is selected then the airflow is distributed to the heat air outlet 122 and the defroster air outlet 116 with a ratio of approximately 80:20. Further, if the heater/defroster mode is selected then the airflow is distributed to the heat air outlet 122 and the defroster air outlet 116 with a ratio of approximately 50:50. Once a mode is selected, however, the ratio of the airflow is fixed and cannot be adjusted. In other words, the volume of airflow exiting the defroster air outlet 116 cannot be adjusted independently of the air exiting heat air outlet 122.
In addition, the temperature of the air exiting the defroster air outlet 116 is the same as the temperature of the air exiting the heat air outlet 122. Thus, the temperature of the air exiting the defroster air outlet 116 cannot be adjusted independently of the air exiting the heat air outlet 122.
Therefore, what is required is an HVAC system that addresses the above mentioned disadvantages.